Studies on the role of bone sialoprotein (BSP) in normal and pathologic mineralization will proceed along several lines. Ultrastructural studies on BSP in rachitic chickens and in chickens with metastatic calcification will be completed. Tissue cultures of bone and cartilage will be used to evaluate the role of vitamin D and its metabolites on BSP synthesis and matrix mineralization. This work will include autoradiography. Finally, work will continue on the isolation and characterization of this BSP antigen.